Abstract

Mutations in the isocitrate dehydrogenase genes IDH1 and IDH2 are among the first genetic alterations observed during the development of lower-grade glioma (LGG). LGG-associated IDH mutations confer gain-of-function activity by converting α-ketoglutarate to the oncometabolite R-2-hydroxyglutarate (2HG). Clinical samples and gene expression data from The Cancer Genome Atlas (TCGA) demonstrate reduced expression of cytotoxic T lymphocyte–associated genes and IFN-γ–inducible chemokines, including CXCL10, in IDH-mutated (IDH-MUT) tumors compared with IDH-WT tumors. Given these findings, we have investigated the impact of IDH mutations on the immunological milieu in LGG. In immortalized normal human astrocytes (NHAs) and syngeneic mouse glioma models, the introduction of mutant IDH1 or treatment with 2HG reduced levels of CXCL10, which was associated with decreased production of STAT1, a regulator of CXCL10. Expression of mutant IDH1 also suppressed the accumulation of T cells in tumor sites. Reductions in CXCL10 and T cell accumulation were reversed by IDH-C35, a specific inhibitor of mutant IDH1. Furthermore, IDH-C35 enhanced the efficacy of vaccine immunotherapy in mice bearing IDH-MUT gliomas. Our findings demonstrate a mechanism of immune evasion in IDH-MUT gliomas and suggest that specific inhibitors of mutant IDH may improve the efficacy of immunotherapy in patients with IDH-MUT gliomas.

Figure 5

(A) Western blotting was performed on GL261-WT and GL261-MUT cell lysates in the presence or absence of 1 μM IDH-C35 and 100 ng/ml recombinant murine IFN-γ. (B) Quantification of Western blot bands by ImageJ. Data represent the mean ± SD of band density/β-actin of 2 to 4 experiments. (C) Western blotting was performed on cell lines treated with 3 mM 2HG. Data shown represent GL261 cells treated with 2HG for 1, 3, or 5 days and NHA and SB28 cells treated with 2HG for 5 days. (D) ImageJ quantification of Western blot bands from C. Data represent the mean ± SD of band density/β-actin band density from 3 independent experiments. (E) ImageJ quantification of Western blot band densities of STAT1, p-STAT1, and IRF1, normalized to β-actin levels for NHA and SB28 cells treated with 2HG. Data are representative of 2 independent experiments with similar results.